Lymphocytotoxic antibodies in systemic lupus erythematosus: evidence for reactivity with i antigen.

Sera from ten patients with systemic lupus erythematosus (SLE) were tested for lymphocytotoxic antibodies (LCA) before and after absorption with cord and adult erythrocytes at 4 degrees C. Seven of the sera showed a significant reduction in cytotoxicity after absorption with the cord erythrocytes, but minimal or no reduction following absorption with the adult red blood cells. Of the remaining three sera, the cytotoxicity was equally reduced by cord and adult red cells in one and was unaffected by absorption in two. Eluates were prepared from the two sera using cord and adult red blood cells. The cytotoxicity of the cord cell eluates was significantly greater than those of the adult red cell eluates. These data indicate that the LCA in most SLE sera have specificity for the i antigen, which is present on lymphocytes and cord erythrocytes.